Dental Bleaching
Tooth discoloration is either extrinsic--on the enamel, or intrinsic--penetrating the tooth dentin. Tea, coffee, nicotine from cigarette smoking and mouth rinses containing active antibacterial agents such as chlorhexidine and cetylpyridinium chloride may cause superficial tooth staining. This type of discoloration is more affected when the dentin is exposed, such as in the case of cracks in the enamel, due to both higher affinity for the discoloring substances to dentin than to enamel and their deeper penetration, so that their removal is extremely difficult. Intrinsic staining is much more complicated because it may involve the dentin more than the enamel. Examples of factors affecting intrinsic discoloration are tetracycline administration during tooth calcification, fluorosis, jaundice during tooth development, trauma which causes internal bleeding, and endodontic materials.
Tooth bleaching has gained increasing interest over the past decade, with the growing awareness of aesthetic dentistry. Modified techniques for whitening discolored teeth have been developed. These techniques involve treatment both at the dental clinic and at home by the patient. Treatment currently carried out by the dentist generally involves acid etching of the enamel with 32% phosphoric acid, followed by bleaching, by applying hydrogen peroxide (30%) to the tooth surfaces. This is followed by application of heat for 20 to 30 minutes, with a heat element or a heat lamp. With severely discolored teeth this method of bleaching is not totally effective, and veneering techniques with concomitant use of opaquers are then necessary. The common bleaching techniques thus typically involve a considerable amount of dental chair time, at a potentially significant cost to the patient.
Home treatment involves the use of 10% carbamide peroxide (urea peroxide) (Haywood et al., Quint. Int. 20(3): 173-176 (1989)). The patient wears a thin vacuform matrix over the teeth, and a reduced concentration of peroxide (which is within safety limits approved by the FDA) is placed within the appliance. The use of 10% urea peroxide as a home treatment is aimed at being significantly time- and cost-saving for the patient (Federal Register, Vol. 47, N9. 101, p. 22, 875 (1982). Haywood ibid. also stressed that using the nightguard, rather than the known rubber dam technique, eliminates the necessity of the pretreatment etching step. It is well known that etching with phosphoric acid or other acids may alter the surface texture of the teeth. Said authors suggest the use of phosphoric acid only as a preservative in the 10% urea peroxide solution, which also contains carbomer 940, glycerine, flavors, phenacetin and trolamine (Proxigel.RTM., Reed & Carnick, Piscataway, N.J.).
Additional home-use tooth bleaching products have also been recently described (Clinical Res. Assoc. 13: 7 (July 1989)). This report describes various commercially available products, all containing 10% carbamide peroxide. DENTA-LITE.RTM. (Challenge Products, Osage Beach, Mo.) is a gel bleaching preparation sold to dentists only. Its recommended use is to wear a tray for at least 14 hours per day, changing the bleach every 1-2 hours for 1 week or longer. DENTL-BRITE.RTM. (Cura Pharmaceutical, Jacksonville Fla.) is a bleaching preparation sold to dentists only. Its recommended use is to wear a tray for 18 hours per day, changing the bleach every 2 hours for 2 weeks. GLY-OXIDE.RTM. (Marion Laboratories, Kansas City, Mo.) is an off-the-counter preparation intended for oral antiseptic uses only. It was not reported as a teeth bleaching agent. REMBRANDT LIGHTEN.RTM. (Dean-Mat, Santa Maria, Calif.) is a gel containing 10% carbamide peroxide and a dentifrice. The gel is used by frequent daily brushes or worn in a mouthguard for at least 12 hours per day. These products have not been reported as bleaching agents. ULTRA LITE.RTM. (Ultra Lite, Inc., Orange Park, Fla.) is a bleaching preparation sold to dentists only. Its recommended use is to wear a tray at least 18 hours per day, changing the bleach every 2 hours for 2 weeks or longer. WHITE & BRITE.RTM. (Omnii International, St. Petersburg, Fla.) is a bleaching preparation sold to dentists only. Its recommended use is to wear a tray 18-20 hours daily, changing the bleach every 2-2.5 hours for about 2 weeks. In this report, the PROXIGEL.RTM. preparation referred to above is also mentioned as an antiseptic and not as a bleaching preparation. This product was originally aimed at improving oral hygiene particularly by removing dental plaque, and is in the form of a solution.
Recently a more sophisticated product has been introduced on the market. This product, sold under the name OPALESCENCE.RTM. (Ultradent Products, Inc., Salt Lake City, Utah) (U.S. and foreign patent applications pending), is presented by its manufacturer as a sustained-release carbamide peroxide gel. This feature increases the efficacy of the product and reduces the appliance wearing time to only at night, which in turn is believed to increase patient compliance. Nevertheless, since the major problem is the appliance, the advantages described with the OPALESCENCE.RTM. product do not totally overcome the problem of patient compliance.
Patient compliance is the major problem (Goldstein et al., Quint. Int. 20: 729 (1989)). The need to wear an appliance for a long time, 12-20 hours per day, discourages many patients from using these products. Others stop care before desired results are achieved (CRA 13(7) (1989)). Other major problems associated with the mouth guard, as reported in said CRA publication, are speech difficulties, irritation to teeth and gingiva, allergic reactions such as tissue swelling, sore throat, bite interference from extended tray use and minor tooth movement. Also said reports refer to possible side effects due to swallowing various ingredients in the formulations over days or weeks, depending on the product and the time worn per day.
One of the primary advantages of the composition of the present invention over this prior art, as will become evident from the detailed description, is patient compliance. It eliminates the necessity of wearing a mouthguard, being a film-forming composition which closely adheres to the dentin layer. This being the case, smaller quantities of chemicals can be applied to the teeth, which is another important advantage.
The use of water-soluble cellulosic polymers, and more particularly, hydroxypropyl cellulose, has been described. For example, WO 90/01046 discloses a composition for in situ formation of medicament films, inter alia, in the oral cavity, comprising hydroxypropyl cellulose (HPC), a weak organic acid (which reaches with the HPC to form a reaction product which is soluble in a non-toxic volatile solvent for the HPC and the reaction product, but is insoluble in body fluids at body temperatures), said non-toxic volatile solvent and a separate medicinal component. This publication does not disclose application for tooth bleaching. According to this publication, the films, once formed, simply re-dissolve upon a further application of the composition to the same site. The film-forming composition according to the present invention simply disintegrates within reactively short periods at time, but not before the release of the bleaching agent has been completed.
Another oral composition for treatment of dental hypersensitivity is disclosed in U.S. Pat. No. 4,645,662 to Nakashimi et al. This publication discloses compositions containing aluminum and a carboxylate compound. Some of the examples describe such compositions also containing hydroxyethyl cellulose, for example, hydroxyethyl- and hydroxypropyl celluloses. These ingredients are described as binders, effective only together with carrageenan, for compositions in the form of paste. This patent does not suggest the liquid polymeric short-term sustained-release bleaching preparation of the present invention.
U.S. Pat. No. 4,713,243 to Schiraldi et al. discloses a bioadhesive extruded film particularly for intra-oral controlled release delivery of a medicament, comprising, inter alia, hydroxypropyl cellulose with an ethylene oxide homopolymer. This extruded preparation is essentially different from the presently claimed in situ film-forming preparation.
U.S. Pat. No. 4,315,779 to Heyd et al. discloses a non-adhesive gel composition for use in improving the fit and adaptation of dentures to the oral cavity, comprising, inter alia, a hydrophilic cellulosic polymer, for example hydroxypropyl cellulose. Also this publication does not suggest the presently claimed dental bleaching composition.
In addition, tooth bleaching preparations contain hydrogen peroxide or peroxy compounds are known in the art. Most of the known preparations are dentifrices, some are gel preparations, as described above.
The stability of urea peroxide is cited in several patents. Japanese Patent 87 280298 A2 and 62 20298 disclose the use of sodium citrate as a stabilizer for urea peroxide in the powder form. U.S. Pat. No. 4,155,738 discloses the use of lignin sulphonide for stabilizing hydrogen peroxide or urea peroxide in a fertilizer composition. Another way of stabilizing urea peroxide in glycerol solution is with succinate anhydride (GB 2,219,504). The use of EDTA for stabilizing urea peroxide in solution has also been disclosed in U.S. Pat. No. 3,624,331, which discloses the stabilizing of urea peroxide for cosmetic use, and in Japanese Patent DM375220.
The use of carbamide peroxide or hydrogen peroxide to treat gingivitis or to prevent dental plaque is well established in the literature. Hydrogen peroxide is recognized as an antimicrobial agent. It is especially useful against anaerobic bacteria, since these cannot produce catalases, which decompose hydrogen peroxide. (Stindt, D. J. et al., Compend. Contin. Educ. Dent. 10: 514-519 (1989). This antimicrobial effect makes hydrogen peroxide a candidate for preventing dental plaque and gingivitis.
However, results of in vivo studies are contradictory. On one hand, it has been demonstrated that mouthwash, containing hydrogen peroxide, prevents plaque and reduces gingivitis (Turner in: Block, S. S., ed., Disinfection, Sterilization, Preservation, Philadelphia, Lea and Febiger, pub., p. 240, (1983); Greenstein and Redman, Compendium of Continuing Education in Dentistry 8: 348-360 (1986), Shipman et al., J. Priodontol. 42: 283-285 (1971) and Wennstron et al., J. Clin. Priodontol. 6: 115-130 (1979)). On the other hand, Zinner et al., J. Preven. Dentistry 2: 13-17 (1980) found no significant reduction in plaque and gingivitis when compared to control groups. One of the possible explanations for this discrepancy is the rapid rate of decomposition of hydrogen peroxide caused by catalases fouled in the oral cavity. Hence a need exists for a more reliable method for the delivery of oxidizing agents for the prevention of plaque and reduction of gingivitis.